Your code shouldn’t care about the actual value of file descriptors. You should treat them as arbitrary integers that could be anything. Programs are allowed to open more than 3 files at a time so of course you should expect to get file descriptors that are outside of the 0-2 range. Anyway, the 0-2 range is used for the the standard files (stdin, stdout, and stderr) so if you open another file I would expect the file descriptor to be a different number.
Your question contains very little information. If you want more help, please read this post first:
–David